Slovaks in Romania were colonised mostly in the late 18th c. and in the first half of the 19th c., most of them from central and eastern Slovakia. In the Banat and southern Crișana ( Arad county ), they were settled in villages that were relatively separate from one another, whereas in Bihor ( Plopiș Mountains area ) and less so in Sătmar they were settled in uniform areas. Those in Bihor and Sătmar are Roman Catholics; in the Banat and Arad area they were originally Lutherans, but Greek Catholics in Scăiuș and Peregu Mare / Vel'ký Pereg (i.e. already Slovakised Ukrainians from easter Slovakia ) and Roman Catholics in Brestovăț / Brestovac. Immediately after the Second World War, a large part of the Slovak population migrated back to Slovakia, as part of a repatriation programme. In some villages in the Banat ( either Slovak originally or non-Slovak ), many Slovaks from Bihor have settled in the first post-War decades.See
below the maps corresponding to the preceding post, for 1869 and
2002. Blue = at least 75%, green = 50-74%, yellow = 25-49%,
red-orange = 10-24%, turquoise = 4-9%. I have also included the villages in the Serbian Banat in the 2002 map ( Serbian census the
same year ).
Sources: http://www.kia.hu/konyvtar, http://webrzs.stat.gov.rs/WebSite/Default.aspx.